CH672558A5 - - Google Patents

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Publication number
CH672558A5
CH672558A5 CH501786A CH501786A CH672558A5 CH 672558 A5 CH672558 A5 CH 672558A5 CH 501786 A CH501786 A CH 501786A CH 501786 A CH501786 A CH 501786A CH 672558 A5 CH672558 A5 CH 672558A5
Authority
CH
Switzerland
Prior art keywords
fuel
coolant
anchor plate
coolant tube
tube
Prior art date
Application number
CH501786A
Other languages
German (de)
Inventor
Harold Lee Nelson
Thomas Gerald Dunlap
Eric Bertil Johansson
Bruce Matzner
Original Assignee
Gen Electric
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Family has litigation
Priority to US06/811,726 priority Critical patent/US4675154A/en
Application filed by Gen Electric filed Critical Gen Electric
Publication of CH672558A5 publication Critical patent/CH672558A5/de
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=25207383&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=CH672558(A5) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.

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Classifications

    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21CNUCLEAR REACTORS
    • G21C3/00Reactor fuel elements and their assemblies; Selection of substances for use as reactor fuel elements
    • G21C3/30Assemblies of a number of fuel elements in the form of a rigid unit
    • G21C3/32Bundles of parallel pin-, rod-, or tube-shaped fuel elements
    • G21C3/322Means to influence the coolant flow through or around the bundles
    • Y02E30/38

Description

DESCRIPTION
In known types of nuclear reactors, for example in a boiling water reactor, such as is used in the nuclear power plant in Dresden near Chicago, Illinois, the reactor core has a plurality of fuel elements which are arranged at a distance from one another and are arranged in a matrix which is arranged in one self-sustaining nuclear fission reaction. The core is contained in a pressure vessel in which it is submerged in a working fluid, such as light water, which serves both as a coolant and as a neutron moderator. Each fuel assembly has a removable tubular flow channel, which is typically approximately square in cross-section and surrounds a matrix of elongated, encased fuel rods containing a suitable fuel, such as uranium or plutonium oxide, and held between upper and lower anchor plates. The fuel assemblies are held in a mutually spaced matrix in the pressure vessel between an upper core lattice and a lower core support. The lower anchor plate of each fuel assembly is provided with a nose piece that fits into a retainer for connection to a supply chamber for pressurized coolant. The nose piece is provided with openings through which the pressurized coolant flows upward through the fuel passage channels to remove heat from the fuel rods. A typical fuel assembly of this type is described, for example, in U.S. Patent 3,689,358. An example of a fuel rod is described in U.S. Patent 3,378,458.
Further information on nuclear reactors can be found, for example, in "Nuclear Power Engineering", M.M. El-Wakil, McGraw-Hill Book Company, Inc., 1962.
A typical fuel assembly is formed, for example, by a matrix of spaced apart fuel rods held between an upper and a lower anchor plate, the rods being several feet long, on the order of 12.7 mm (one-half inch) in diameter. have a mutual distance of a few millimeters. To create a proper coolant flow past the fuel rods, it is important to keep the fuel rods a fixed distance away and to prevent them from bending and vibrating during reactor operation. Several fuel rod spacers, spaced apart along the length of the fuel assembly, are provided for this purpose. These spacers are described, for example, in U.S. Patent 4,508,679.
In a typical boiling water reactor, the fuel elements are spaced from one another, as described, for example, in US Pat. No. 3,802,995. This leaves gaps or channels between the fuel assemblies that are relatively cool
Water moderator are filled. The peripheral fuel rods of the fuel assemblies are therefore exposed to neutrons of relatively low thermal energy, which are more likely to cause fission in the fuel, whereas the fuel rods in the inner region of the fuel assemblies are exposed to neutrons with higher thermal energy.
In addition, boiling in the upper part of the boiling water reactor core reduces the neutron moderation in the upper region of the fuel elements.
The peripheral fuel rods tend to produce relatively more power because they are exposed to a relatively larger amount of low energy thermal neutrons and therefore have a higher heat flow than the fuel rods in the inner region. To aid cooling of the peripheral fuel rods and to mix the water flow passing through the fuel assembly, inwardly curved flow deflector flaps can be added to the peripheral tether of the fuel rod spacers. Such baffles are described, for example, in US Pat. No. 4,061,536.
An uneven moderator / fuel ratio can be mitigated by using "partial length" fuel rods that only extend over the lower (bubble free) region of the fuel assembly, as described, for example, in U.S. Patent 2,998,367.
To alleviate the unequal neutron moderation caused by the water channels surrounding each fuel assembly and by boiling in the top of the reactor core, one or more central fuel rods can be replaced with water-carrying tubes that deliver bubble-free water to the top of the fuel assembly transport. Such arrangements are described, for example, in the aforementioned U.S. Patents 3,802,995 and 4,420,458. According to these two US patents, the water pipes have approximately the same diameter as the fuel rods.
The idea of using a large water pipe (e.g. one that replaces four fuel rods) is also known, for example, from US Pat. No. 3,132,076 (Fig. 5) and from US Pat. No. 3,808,098.
The use of such a large water pipe, however, brings with it problems which are neither addressed nor solved in the prior art. Such a large water pipe is inherently quite stiff (compared to the smaller diameter fuel rods). When such a large water pipe is attached to the lower anchor plate, it is therefore a relatively rigid part that crosses the fuel assembly through the passages in the fuel rod spacers.
When the fuel assembly is subjected to transverse loads, for example during an earthquake, it can generally be assumed that the lower anchor plate and the nose piece of the fuel assembly remain seated in their holding bush, whereas the upper part of the fuel assembly can undergo a transverse displacement. In such a case, the relatively stiff, large water pipe can subject the fuel rod spacers to transverse loads that exceed the load capacity of the spacers (especially the lowest spacers).
The object of the invention is to provide an improved nuclear reactor fuel element compared to existing designs, which strives to compensate for neutron moderation, improve heat transfer and minimize the coolant pressure drop.
A fastening arrangement for a water pipe is to be created which avoids excessive transverse loads on the fuel rod spacers.
According to the invention, this object is achieved by the features in the characterizing part of the first claim.
The fastening part created thereby allows a seitli5
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che displacement of the upper end of the water pipe without exerting excessive forces on the fuel rod spacers. The water tube is provided with radially extending tabs above and below each spacer to hold the spacers in their axial positions.
The fastener may be attached at its lower end to the lower anchor plate, the water pipe may end at or near the upper end of the fuel zone, and the area of the upper anchor plate above the water pipe may be open to reduce the coolant pressure drop.
Furthermore, the water pipe can be held between the upper and lower anchor plate. The flexible fastener in this embodiment is in the form of a tube that has openings near the lower end of the fuel assembly into which supercooled water can flow and then flow up into the water pipe that has water outlets at or near the upper end of the fuel zone. An upper holding part or an extension of smaller diameter, which is attached to the upper end of the water pipe, engages a holding cavity in the upper anchor plate.
Forced fuel rod spacers for low coolant pressure drop, coolant flow deflecting tubes on the peripheral tether of the spacers for the coolant mixing, and improved heat transfer from the surfaces of the peripheral fuel rods, and part length fuel rods that tend to be the moderator / fuel- Compensate ratio and reduce the coolant pressure drop in the fuel assembly.
Exemplary embodiments of the subject matter of the invention are described in more detail with reference to the drawing. Show it:
1 shows a longitudinal section through a fuel assembly with a fastening device for a water pipe,
2 is a schematic representation of the lateral force exerted by the water pipe on the fuel rod spacer.
3 is a side view, partly in section, of the fastening device for the water pipe in the embodiment according to FIG. 1,
4 shows a plan view of the upper anchor plate of the fuel assembly according to FIG. 1,
5 is a schematic illustration of the fastening device, which illustrates the reduction of the lateral forces on the fuel rod spacer,
6 is a side view, partly in section, of a variant of the fastening arrangement according to FIG. 1,
7 shows a longitudinal section through a fuel assembly with a further embodiment of the fastening arrangement,
8A and 8B are a side view, partly in section of the fastening arrangement according to FIG. 7, and
Fig. 9 is a plan view of a fuel rod spacer for receiving the water pipe.
1, a fuel assembly 21 has a plurality of fuel rods 22 which are arranged at a mutual spacing and are held between an upper anchor plate 23 and a lower anchor plate 24. (An 8x8 matrix is shown, but "only some of the fuel rods 22 are shown for the sake of clarity.) The fuel rods 22 are passed through a plurality of fuel rod spacers 26 (only one of which is shown in FIG. 1), which form an intermediate holder to keep the elongated fuel rods apart and prevent them from vibrating sideways.
Each fuel rod 22 consists of an elongated tube that contains a column of nuclear fuel 27. A plenum at the top of the fuel rod 22 contains a spring 25 that holds the fuel column in place.
The fuel rods 22 are closed by an upper end plug 28 and a lower end plug 29. The lower end plugs 29 are provided with a cone for holding and supporting in cavities 31 in the lower anchor plate 24. The upper end plugs 28 are provided with extensions 32, the upper ends of which fit into holding cavities in the upper anchor plate 23.
Of the holding cavities 31 in the lower anchor plate 24, several (e.g., selected peripheral cavities) are threaded to receive the end plugs of anchoring fuel rods 22 'that have threaded end plug shafts 29'. Extensions 32 'of the end plugs 28 of the same fuel rods are elongated so that they can be passed through the cavities in the upper anchor plate 23, and are provided with threads for receiving retaining nuts 33. Extension springs 34 are arranged on the extensions 32 between the upper end plugs 28 and the upper anchor plate 23. In this way, the upper and the lower anchor plate and the fuel rods are combined into one piece.
The fuel assembly 21 also has an open-ended, thin-walled, tubular flow channel 36 which has a substantially square cross section and is dimensioned such that it has a sliding fit over the outer sides of the upper anchor plate 23 and the lower anchor plate 24 and the spacers 26 so that the channel 36 can be easily assembled and removed. At the upper corner of the channel 36, a tab 37 is attached, through which the channel 36 is attached to a post 38 of the upper anchor plate 23 by a screw 39. Since the channel 36 is not attached to the lower anchor plate 24, the upper end of the channel 36 can move freely with respect to the lower anchor plate 24 in the event of a movement of the upper end of the fuel assembly 21.
The lower anchor plate 24 is provided with a downwardly extending nose piece 41 which is conical in order to grip a fuel assembly holding bushing (not shown). The lower end of the nose piece 41 is provided with an opening 42 for receiving pressurized water (as a coolant / moderator) so that it can flow upwards between the fuel rods.
The fuel rod spacers 26 are preferably formed as tubular ferrules because of their favorable low coolant pressure drop, as shown and described in detail in the aforementioned U.S. Patent 4,508,679. In addition, the peripheral retaining band 44 of the spacer 26 is advantageously provided with coolant flow deflecting flaps 46 which extend upward and are bent inwards (cf. also FIG. 9). The flow deflecting flaps 46 seek to deflect the relatively cooler water moving upward along the inner surface of the flow channel 36 toward the surface of the outer or peripheral fuel rods 22. This supports cooling and heat transfer from these fuel rods and allows them to produce more heat without exceeding thermal limits.
To assist in balancing the neutron moderation, the fuel assembly 21 is provided with a large water pipe 47 for transporting relatively cold water up through the central region of the fuel assembly. 1 (see also FIG. 9), the large water pipe 47 takes up the space of four fuel rods. As already briefly explained above, it is a problem when using a large water pipe to create a fastening device which prevents the spacers from being overloaded by the large water pipe in the event of a lateral displacement of the fuel element 21, for example during an earthquake.
Before the fastening device for the large water pipe is described, the Pro5
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blems referred to Fig. 2. 2 schematically shows a lower anchor plate 241, to which a large water pipe 471 is rigidly attached, which is led through by a spacer 261, which is arranged at a distance L from the lower anchor plate 241.
If the fuel assembly to which these parts belong is laterally displaced at its upper end and the large water pipe 471 is displaced from its center line by a distance d (measured in the axial center line of the spacer 261), then the large water pipe becomes one Angle A is bent, with the result that a force Fi is applied to the spacer 261.
The resulting side load Fi of the spacer is determined by the following relationship:
12 EGG LA
Fi = (d) (1)
L3 2
in which:
E is the modulus of elasticity of tube 471,
I is the section modulus of tube 471,
L is the distance from the anchor plate 241 to the axial center line of the spacer 261,
d is the lateral displacement of tube 471 from its normal centerline (measured in the axial centerline of the bottom spacer 261) and A is the deflection angle.
For a large zirconium alloy water pipe 471 with an outer diameter of approximately 3.4 cm (1.35 inches) and a wall thickness of approximately 1 mm (0.04 inches), a deflection d of approximately 1.3 cm (0.5 inches) results ) with a length L of about 50.8 cm (20 inches) a spacer side load Fi of about 73 kp (160 lbs). This greatly exceeds the normal design resilience of the spacer 261, which is in the order of a maximum of 6.8 kp (15 lbs).
In order to avoid such excessive loads on the spacers 26, the large water pipe 47 according to the invention is fastened to the lower anchor plate 24 using a relatively flexible fastening part 48, which is shown in FIG. 1 and in more detail in FIG. 3. In this version, part 48 is in the form of a rod having an enlarged or flanged lower end part 49 which is tapered at its lower end and inserted into a similarly conical cavity 50 in lower anchor plate 24. The flange-provided end part 49 is provided with a threaded bore for receiving a screw 52, by means of which the fastening part 48 is fastened to the anchor plate 24.
At its upper end the part 48 is provided with an upper flanged part 53 which has an outer surface which has been machined to receive the lower end of the large water pipe 47 to which it is fixed by welding or the like is. The flanged part 53 has passages 54 for introducing water into the tube 47. The lower outer surface of the flanged portion 53 has been machined to receive a downwardly extending tubular skirt 56 attached thereto by welding or the like. The bezel 56 ensures that only water near the lower end of the fuel assembly, where it is relatively small, is let into the large water pipe 47.
In the axial position of each spacer 26, the water pipe 47 is provided with two mutually spaced and radially extending lugs 57 which limit the axial movement of the spacers 26 and thus hold them in the correct axial position. (The way in which the spacers 26 are fastened to the water pipe 47 is explained in more detail below.)
According to the illustration in FIG. 1, the large water pipe 47 extends only up to approximately the upper end of the fuel 27 in the fuel rods 22, since bubble-free water is not required for additional neutron moderation above this point. In addition, as shown in Fig. 4, the webs and eyes, which would be required for the four fuel rods, which replace the large water pipe 47, have been omitted from the upper anchor plate 23 around a large opening 58 for the escape of steam and water to create the fuel assembly. The end of the water pipe 47 at the top of the fuel column and the opening 58 in the top anchor plate 23 both contribute to reducing the coolant pressure drop as the coolant passes through the fuel assembly 21.
FIG. 5 schematically illustrates the effect of the flexible fastener 48 in preventing excessive lateral forces on the spacers 26. Since the fastener 48 is designed to bend much more easily than the water pipe 47, it can be assumed that the part 48 will absorbs the entire bending load.
The resulting spacer side load F2 is then determined by the following relationship:
d-LiA
F2 =
(L2) 3 (L, L22) (2)
■ +
3 (EI) 2 (EI)
in which:
E is the elastic modulus of the fastening part 48,
I is the section modulus of the fastening part 48,
d is the postulated transverse displacement of the tube 47, for example during an earthquake, from its normal center line (measured in the axial center line of the lowest spacer 26),
Li + L2 is the distance from the lower anchor plate 24 to the axial center line of the spacer 26,
L2 is the length of the flexible fastener 48, and
A is the bending angle.
Using this relationship, various combinations of materials, diameters, and lengths for the fastener 48 can be calculated to determine a practical combination that will suitably limit the side force F2 on the spacer. For example, a practical combination has been found from a piece 48 of zirconium alloy approximately 0.25 inches in diameter and approximately 5 inches in length. For a postulated displacement d of 1.27 cm (0.5 inches), this limits the side force on spacer 26 to about 2.27 kp (5 lbs), which is well within the spacer design limits.
An alternative embodiment of the water pipe mounting part is shown in FIG. 6. In this version, a flexible fastening part 481 has the shape of a tube and is provided at its lower end with a conical end plug 491, which is fastened to the lower anchor plate 24 by the screw 52. A diameter transition part 531 is fastened to the upper end of the fastening part 481, which in turn is fastened at its upper end to the large water pipe 47 by welding or the like.
A plurality of holes 59 for introducing coolant into the fastening part 481 and from there into a passage 61 which leads into the large water pipe 47 are formed in the lower end of the fastening part 481. A practical diameter, wall thickness and length that give spacer side loading within the design limits can be determined using equation (2) given above. For example
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tubular zirconium alloy fastener 481 with an outer diameter of about 1.5 cm (0.60 inches) and a wall thickness of about 0.76 mm (0.03 inches) and a length of the order of 38 cm (15 inches) getting produced.
An alternative embodiment of the fastening device for a large water pipe is shown in FIG. 7 and in FIGS. 8A and 8B to be considered together. (In these figures, the same parts have the same reference numerals as in the previous figures.)
A fuel assembly 211 of this embodiment is similar to the previously described fuel assembly 21 of FIG. 1 except for the attachment device for the large water pipe 471. At its lower end, the water pipe 471 (see FIG. 8B) is on the lower anchor plate 241 by a tubular flexible Supported part 482 supported, which corresponds in design and structure to the previously described fastening part 481 of FIG. 6. The difference is that it is not attached to the lower anchor plate with a screw, but that the lower end plug 492 of this embodiment is provided with an elongated, downwardly extending stem 62 that fits into an elongated, matching cavity 63 in the lower anchor plate 241 is fitted. The shaft 62 is here, for example, square in cross-section and the cavity 63 has a matching shape to prevent rotation of the water pipe which could cause the spacer retaining tabs to disengage from the spacer 26, which is described in greater detail in the above-mentioned U.S. Pat. PS 3 802 995 is explained. The stem 62 and cavity 63 are elongated compared to the lower end plug shafts of the fuel rods 22 to prevent disengagement from the lower anchor plate 241 in the event of a different axial expansion with respect to the fuel rods, which is more fully described in the aforementioned U.S. Patent 4,420,458.
The support member 482, which is attached at its lower end to the end plug 492, is attached at its upper end to the large water pipe 471 by means of the transition part 531, the holes 59 and the passage 61 admitting water into the pipe 471.
A practical design for the flexible support member 482 (i.e. its diameter, wall thickness and length for a selected material) can be determined using equation (2) above. In a practical example, part 482 is made of a zirconium alloy with an outer diameter of about 1.5 cm (0.60 inches), a wall thickness of about 0.76 mm (0.03 inches) and a length of about 38 cm (15 Inch).
According to the illustration in FIG. 8A, the large water pipe 471 ends in the region of the upper end of the fuel 27 (FIG. 7) and is provided at its upper end with an upper holding part which has a transition piece 64 to which it can be welded or Like. is attached. A plurality of holes 66 are formed in the upper end of the water pipe 471, which form an outlet for the water flowing therein near the upper end of the fuel 27, since additional neutron moderation above the fuel 27 is not necessary, and the end of the large water pipe 471 reduced the coolant pressure drop at this level.
Attached to the upper end of the transition piece 64 is an upper holding part or an extension 67, which is shown as a tube section, which preferably consists of a zirconium alloy and has a diameter which is similar to that of the fuel rods 22 or the supporting part 482. (Holes 68 in the extension tube 67 rid the tube of an external / internal pressure difference.) At its upper end, the extension 67 is provided with an end plug 69, which is provided with an elongated shaft 71 which extends through a
Holding cavity extends in the upper anchor plate 231. An expansion spring 341 is arranged on the shaft 71 between the end plug 69 and the upper anchor plate 231. The stem 71 extends beyond the upper anchor plate to prevent disengagement therefrom in the event of a different expansion with respect to the fuel rods, and the spring 341 may be provided with several closely spaced turns to limit the upward movement of the water pipe as explained in the aforementioned U.S. Patent 4,420,458.
An advantage of this embodiment of fastening the large water pipe according to FIG. 7 (compared to the embodiment according to FIG. 1) is that the large water pipe can be installed and removed without the underside of the lower anchor plate 241 having to be accessible.
The use of partial length fuel rods 221 is also shown in FIG. The sealed fuel rods 221 can be about one third to about two thirds the length of the normal or full length fuel rods 22, but are preferably about half that length. In order to secure the fuel rods 221 in the fuel assembly 211, the shafts of the lower end plugs 291 can be threaded, which fit into threaded holding cavities in the lower anchor plate 241. These threads can be provided with a cone for secure attachment.
FIG. 9 shows a top view (in which some parts are omitted) of the spacer 26, which shows, among other things, a preferred radial position of the part-length fuel rods 221. The fuel rods 221 are preferably arranged inward of the peripheral fuel rods. In the illustrated case, four part-length fuel rods 221 are arranged immediately inward of the corner fuel rods 22.
The benefits of the partial length fuel rods are described in more detail in the above-mentioned U.S. Patent 2,998,367. The increase in the coolant flow cross section in the upper part of the fuel assembly reduces the coolant pressure drop. Reducing the amount of fuel in the top of the fuel assembly where the cold shutdown reactivity peaks increases the cold shutdown reactivity margin.
Further features that are shown in FIG. 9 are the coolant flow deflection flaps 46 and the modification of the spacer 26 for receiving the large water pipe 47/471. (Only a few of the ferrules 51, in simplified form, forming the spacer 26 are shown in Figure 9. A more detailed description of such a spacer and its details can be found in the above-mentioned U.S. Patent 4,508,679.)
To accommodate the large water pipe 47, the four central clamps of the spacer 26 have been omitted. Two brackets 72, which are provided with an overall M-shaped cross-section and extend over the length of the clamps, are each fastened to one of two spaced-apart clamps 51, which surround the water pipe 47 (for example by welding). The brackets 72 serve several purposes. They reinforce the spacer 26. They serve as relatively rigid stops for holding the water pipe 47 laterally, and one of the brackets 72 cooperates with the spacer retaining lugs 57 in order to hold the spacer 26 in its correct axial position.
To better illustrate the latter function, a retaining lug 57 is shown with dashed lines in a first radial position 73 between the brackets 72. In this radial position, the water pipe 47 can be inserted through the spacer 26 until the spacer is between two retaining lugs 57 (see e.g. Fig. 3). After reaching this axial position, the water pipe 47
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and the spacer 26 is rotated (45 °) with respect to one another until one of the brackets 72 is between the pair of lugs 57 in the radial position 74, in which the lugs 57 can now grip the bracket 72 by the axial displacement of the spacer 26 to limit.
In the embodiment according to FIG. 1, the water pipe 47 is fastened in its spacer holding position by the fastening screw 52. In the embodiment according to FIG. 7
rotation of the water pipe 471 is prevented by inserting its molded end plug shaft 62 (FIG. 8B) into the molded cavity 63 of the lower support plate 241.
In contrast to the brackets 72, a further pair of brackets 76 (which are generally U-shaped) are fastened between adjacent clamps 51. A spring member 77 is attached to each bracket 76, which prevents vibration by keeping the water pipe 47 in contact with the brackets 72.
4 sheets of drawings

Claims (18)

  1. 672 558
    2nd
    PATENT CLAIMS
    1. Nuclear reactor fuel element, characterized by: a plurality of elongated fuel rods (22), each one
    Contain fuel column (27);
    a holding device which forms a plurality of holding positions for holding the fuel rods (22) at a mutual spacing in a matrix, with a lower anchor plate (24) which engages the lower ends of the fuel rods (22);
    a nose piece (41) protruding from the lower anchor plate (24) and forming a coolant receiving chamber;
    an elongated coolant tube (47) extending up through the fuel assembly (21) and occupying the space of a plurality of fuel rods (22), the coolant tube having an opening at its lower end for receiving coolant and an opening at its upper end for dispensing of coolant has;
    at least one spacer (26) axially disposed between the upper and lower ends of the fuel rods (22) for laterally holding the fuel rods and the coolant tube (47); and a fastener (48) for the coolant tube (47), the lower end of the fastener (48) engaging the lower anchor plate (24) and the upper end of the fastener (48) being fastened to the lower end of the coolant tube (47) and wherein the fastening part (48) is relatively flexible in comparison to the coolant tube (47), as a result of which excessive lateral forces on the spacer (26) are avoided in the event of a lateral displacement of the upper end of the coolant tube (47).
  2. 2. Fuel element according to claim 1, characterized in that the fastening part (48) is provided with an enlarged conical lower end (49) which surrounds a conical holding cavity (50) in the lower anchor plate (24) and on this with a screw (52) is attached.
  3. 3. Fuel element according to claim 1 or 2, characterized in that the fastening part (48) is provided with an enlarged upper end (53) which is fastened to the lower end of the coolant tube (47) and with at least one passage (54) for admission of coolant is provided in the coolant pipe (47).
  4. 4. The fuel assembly of claim 3, characterized by a tubular skirt (56) attached to the enlarged upper end (53) of the mounting member (48) and extending downwardly around the mounting member, thereby providing only coolant near the lower end of the fuel assembly (21) is let into the coolant pipe (47).
  5. 5. Fuel element according to one of claims 1 to 4, characterized in that the coolant tube (47) is open at its upper end and that the upper end up to approximately the height of the upper end of the fuel column (27) in the fuel rods (22 ) extends.
  6. 6. Fuel assembly according to one of claims 1 to 5, characterized in that the fastening part (48) is in the form of a rod made of zirconium alloy with a diameter of approximately 0.6 cm (0.25 inches) and a length of approximately 12.7 cm (5 inches).
  7. 7. Fuel element according to claim 1, characterized in that the fastening part is a tubular fastening part (481) with an outer diameter of approximately 1.5 cm (0.60 inches),
    a wall thickness of about 0.76 mm (0.03 inches) and a length of about 38 cm (15 inches), which has multiple holes (59) near its lower end for admitting coolant into the fastener and thence into the coolant pipe (47) is provided.
  8. 8. Fuel element according to one of claims 1 to 7, characterized by an upper anchor plate (23) which detects the upper ends of the fuel rods (22) and has an opening (58) above the coolant tube (47) which has a cross section which is at least equal to the cross section of the coolant tube (47).
  9. 9. Fuel assembly according to claim 1, characterized by an upper anchor plate (23) which detects the upper ends of the fuel rods (22), and by a holding part (67) for the coolant tube (47), the upper end of the holding part (67) the upper anchor plate (23) is gripped and the lower end of the holding part (67) is fastened to the upper end of the coolant tube (47).
  10. 10. The fuel assembly according to claim 9, characterized in that the coolant tube (47) ends in the vicinity of the upper end of the fuel column (27) in the fuel rods (22) and that the holding part (67) has a diameter which is substantially smaller than that Diameter of the coolant tube (47).
  11. 11. The fuel assembly according to claim 10, characterized by a diameter transition piece (64) at the lower end of the holding part (67), which is fixed to the upper end of the coolant tube (471), by an end plug (69) at the upper end of the holding part ( 67), the end plug being provided with an elongated shaft (71) of reduced diameter, by an expansion spring (341) arranged on the elongated shaft between the lower end of the end plug and the upper anchor plate (231), and through a plurality of holes (66), which are formed in the upper end of the coolant tube (471) approximately at the height of the upper end of the fuel column (27) in the fuel rods (22).
  12. 12. The fuel assembly according to claim 11, characterized in that the fastening part for the coolant tube has:
    a pipe section (482) with a diameter that is substantially smaller than the diameter of the coolant pipe (471);
    a diameter transition piece (531) attached at its upper end to the lower end of the coolant pipe (471) and at its lower end to the pipe section (482);
    an end plug (492) attached to the lower end of the tube section (482) and engaging the lower anchor plate (241), the end plug being provided with an elongated elongated shaft (62) having a different circular cross-section which fits into one matching cavity (63) is fitted in the lower anchor plate (241), thereby preventing the fixing member and the coolant tube (471) from rotating from a predetermined radial position;
    a plurality of holes (59) formed in the lower end of the tube section (482) for admitting coolant therein; and an axially extending passage (61) formed in the diameter transition piece (531) for passing coolant from the pipe section (482) into the coolant pipe (471).
  13. 13. A fuel assembly according to claim 12, characterized by two spacer retaining lugs (57) which are axially spaced and are attached to the coolant tube (471) and extend radially above and below the spacer (26) in order to limit its axial displacement when the coolant tube (471) is in the predetermined radial position.
  14. 14. Fuel assembly according to one of claims 1 to 12, characterized by two axial spacing spacer retaining lugs (57) which are fastened to the coolant tube (47) and extend radially above and below the spacer (26) in order to axially displace them limit when the coolant tube (47) is in a predetermined radial position.
  15. 15. Fuel element according to one of claims 1 to 14, characterized in that the spacer (26) is designed as a ferrule and has a peripheral retaining band (44) with
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    40
    45
    50
    55
    60
    65
    3rd
    672 558
    extending upward and inwardly curved coolant flow deflection flaps (46) is provided.
  16. 16. Fuel element according to one of claims 1 to 15, characterized by at least one partial length fuel rod (221) which is fastened on the lower anchor plate (24) and between one third and two thirds the length of the full length fuel rods (22 ) extends.
  17. 17. The fuel assembly according to claim 16, characterized in that the partial length fuel rod (221) has a length of approximately half of the full length fuel rods (22).
  18. 18. Fuel element according to claim 16 or 17, characterized by four part-length fuel rods (221), which are each arranged in a fuel rod position immediately inward of the corner fuel rods (22) of the fuel element (21).
CH501786A 1985-12-20 1986-12-16 CH672558A5 (en)

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US06/811,726 US4675154A (en) 1985-12-20 1985-12-20 Nuclear fuel assembly with large coolant conducting tube

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CH672558A5 true CH672558A5 (en) 1989-11-30

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CH (1) CH672558A5 (en)
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ES (1) ES2003983A6 (en)
IT (1) IT1199824B (en)
SE (2) SE464841B (en)

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DE3641974A1 (en) 1987-06-25
ES2003983A6 (en) 1988-12-01
DE3645230C2 (en) 1993-09-02
SE503854C2 (en) 1996-09-23
SE464841B (en) 1991-06-17
IT1199824B (en) 1989-01-05
JPH0778548B2 (en) 1995-08-23
SE9003877D0 (en) 1990-12-05
SE9003877L (en) 1990-12-05
JPS62177487A (en) 1987-08-04
US4675154A (en) 1987-06-23
IT8622784D0 (en) 1986-12-19
SE8605427L (en) 1987-06-21
SE8605427D0 (en) 1986-12-17
DE3641974C2 (en) 1992-07-23

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